The present application claims the priority of Japanese Patent Application No. 2001-013621, filed in Japan on Jan. 22, 2001, the entire contents of which is hereby incorporated herein by reference.
1. Technical Field of the Invention
The invention concerns a method for the formation of Cu (copper) wiring films where the adhesion of the copper film to a base diffusion barrier film is improved in a method for the formation of copper wiring where a copper film is formed on the diffusion barrier film which has been formed on an insulating film which has been formed on a substrate which is being processed.
2. Discussion of Related Art
Cu (copper) has been used for wiring material for high performance semiconductor devices which have appeared in recent years. This is because Cu has a lower resistance than Al (aluminum) and is more resistant to the phenomena known as stress migration and electro-migration which are dominated by the diffusion behavior of the metal atoms from which the wiring is constructed.
A method in which a pattern of wiring and connecting holes (via holes) or contact holes is formed on an insulating film and then a barrier layer is formed, a copper (Cu) film is embedded in the pattern concavities and the excess copper film is removed by CMP (chemico-mechanical polishing) is used for the formation of Cu wiring of this type.
For example, it is proposed in Japanese Unexamined Patent Application Laid Open H10-79389 that, when forming a thin copper film with the CVD method on an insulating film, which has been formed on a substrate, and in which concavities have been established and the copper material of the thin copper film is made to fill the concavities as a method of forming copper wiring, the CVD process should be divided into two parts. A heat treatment which fluidizes the thin copper film which has been formed in the first process should be established between the divided CVD processes.
In the past, the embedding technique where a barrier layer is formed by PVD and a seed film of copper (a base film to provide an electrode for electro-copper plating) is formed by PVD and electroplated with Cu is widely used to form the wiring films of semiconductor devices.
For example, in Japanese Unexamined Patent Application Laid Open H11-135504 there is proposed for the purpose of forming a copper film which has good electro-migration resistance a method for the manufacture of semiconductor devices comprising a process whereby grooves are formed in an insulating film which has been formed over a semiconductor substrate, a process whereby a first copper film is formed in the grooves on the insulating film by sputtering using a target, a process whereby the first copper film is heated and caused to re-flow, a process whereby a second copper film is grown by plating or CVD (chemical vapor deposition) on the first copper film, and a process whereby, on removing by means of CMP the second copper film and the first copper film on the insulating film, at least the first copper film is left behind in the grooves.
Embedding by copper electroplating is widely used as a low cost technique but, as mentioned above, a seed film must be formed beforehand as an electrode. Hence, as the miniaturization of semiconductor devices continues in the future the CVD method which provides good coverage is being put forward as an effective candidate for the formation of the Cu seed films instead of the PVD method.
In recent years it has been recognized that as wiring becomes finer the formation of seed films with the CVD method which provides good coverage has advantages.
In the method disclosed on Japanese Unexamined Patent Application Laid Open H11-135504 referred to earlier, the copper film which has been formed by sputtering is temporarily fluidized by heating (annealing). However, with the need for thinner films in the future there is a problem in that as the Cu seed films which are formed with the CVD method become thinner it is possible that they may agglomerate as a result of this heating (annealing). If agglomeration of the Cu seed film occurs at the formation stage and the base (barrier film) is exposed here and there where there is no film then another problem arises in that voids (gaps) will be present after the subsequent embedding process with copper electroplating.
Furthermore, in the method for the manufacture of semiconductor devices with a process in which a first copper film is formed as a seed film using the CVD method and a second thin copper film is formed by plating using the first copper film as an electrode, for example, there has been a problem in the past in that the adhesion of the Cu layer which forms the interface with the base film for diffusion barrier purposes such as TiN is poor. Consequently, problems have arisen with the fact that peeling of the Cu film from the base film for diffusion barrier purposes such as TiN has inevitably occurred. In the polishing process (CMP Process) after forming a copper wiring film with the CVD method.
Thus, the present invention is intended to provide a method for the formation of copper wiring films which makes the most of the advantages of the CVD method which provides good coverage with which, while forming the thin copper film which forms the seed film by means of the CVD method, the adhesion of the thin copper film which is formed by CVD and the base film for diffusion barrier purposes can be improved easily using the technique known as seed film annealing.
In order to resolve the aforementioned problem, a method for the formation of copper wiring films, comprises the steps of forming a first copper film by means of a CVD method on an insulating diffusion barrier film; heating the first copper film to a temperature within the range from 200 to 500xc2x0 C.; and subsequently forming a second copper film on the first copper film by a plating method using the first copper film as an electrode.
Another method for the formation of copper wiring films comprises the steps of forming a first copper film on an insulating diffusion barrier film; forming a second copper film on the first copper film by a plating method using the first copper film as an electrode; and heating the first copper film to a temperature within the range from 200 to 500xc2x0 C.
Here, the heating temperature in the heating (annealing) process is set within the range from 200 to 500xc2x0 C. because the copper film deposition conditions with the CVD method generally include a temperature of about 200xc2x0 C. and if it is not heated to a temperature above this level then the adhesion-improving effect brought about by the inclusion of the heating (annealing) process is unsatisfactory, while if the temperature exceeds 500xc2x0 C. there is a risk of heat causing damage to the substrate, and this is undesirable.
Moreover, a heating temperature within the range from 350 to 450xc2x0 C. is more desirable as a better improvement in adhesion can then be attained by the heating (annealing) process.
If, in the aforementioned copper wiring film forming method of the invention, the atmosphere in the heating (annealing) process is at a pressure of at least 10 KPa then there is no fluidization or agglomeration on heating (annealing) under the aforementioned temperature conditions of 200 to 500xc2x0 C. and the adhesion can also be improved.
If a second heating (annealing) process is carried out after the second copper wiring film forming process in the aforementioned copper wiring film forming method of the present invention then the reliability of the wiring is increased and, moreover, there is a further advantage in respect of the improvement in adhesion.
Furthermore, the thickness of the first copper film which is formed in the first copper film forming process in the aforementioned copper wiring film forming method of this invention is preferably not more than 100 nm.
The first copper film is known as the so-called seed film, and it is made as thin as possible from the viewpoint of cost provided that it has sufficient thickness to function as an electrode for the subsequent electroplating process, and generally it has a thickness of from 20 nm to about 100 nm since this is advantageous in terms of the production costs.
Thus it is possible to improve adhesion without fluidization or agglomeration even if the first copper film is thin at not more than 100 nm as indicated above by means of a first heating process which is carried out at a heating temperature within the range (from 200 to 500xc2x0 C.) used in the copper wiring film forming method of this invention (and most desirably at a temperature of from 350 to 450xc2x0 C.), and preferably by means of a first heating process in the aforementioned temperature range which is carried out in an atmosphere at a pressure of at least 10 Kpa.